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Room Acoustic Parameters Analysis Software

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Room Acoustic parameters analysis with AERAP

Photo of ROOM IR

AERAP is software which computes the room acoustic parameters such as the reverberation time and the intelligibility for music and speech, using the room impulse responses measured by AEIRM.
It had been usual to rely on the evaluation of designer's or engineer's "ear" in room acoustics. In the subjective evaluation like these, the expression such as "clear" or "clean" sound image are commonly given. So, similar to others, there is a need for constructing a quantitative parameter which corresponds well to subjective feelings.

Various room acoustic parameters

Photo of AERAP SoftwareWe can analyze the impulse responses measured by AEIRM, to calculate various room acoustic parameters. AERAP has a filtering function with 1/1, 1/3 octave frequency bands, and can calculate almost all the parameters which have been proposed in the room acoustics research. The definition of these acoustic parameters have been provided in ISO 3382 Acoustics - Measurement of the reverberation time for rooms with reference to other acoustical parameters.

Room acoustic parameters

Echo Time Pattern
(ETP)
Echo time pattern is the time domain data after processing impulse response with a band pass filter.
In this software, the data are saved in the impulse response file (IMP file) format.
This data is the fundamental data to calculate other parameters.
Reverberation Time
(RT)
By using the Echo Time Pattern with the integrating impulse response method, the sound pressure level decay curve can be computed.
The reverberation time is defined as the time for the energy to decay by -60 dB from stationary sound pressure level.
Early Decay Time
(EDT)
It indicates the initial decay time by 10dB after the arrival of direct sound.
In case the decay curve is completely exponential, it is exactly the same value as the reverberation time.
Strength (G) It is the ratio of the energy calculated from the impulse response at a receiving point and the energy which is measured at the point of 10 m distant from the same sound source in an anechoic chamber.
This parameter is used commonly to show the distribution of the sound pressure level inside a hall by corresponding to the distance decay of the sound pressure level in a free sound field.
From this definition, the impulse response data which was measured at the point of 10 m distant from the sound source in an anechoic room is needed to calculate it.
Clarity (C80, C) Clarity is proposed for indicating the clarity of music.
It is defined by the ratio between the energy which comes to 80 ms after the arrival of direct sound and the energy after that.
Deutlichkeit
(D50, D)
Deutlichkeit is proposed as the parameter which indicates the clarity of speech.
It is defined by the ratio between the energy until 50 ms after the arrival of the direct sound and the whole energy including the direct sound.
Center Time (ts) This is the "center of gravity" of the inpulse response in time domain.
It is reported that the syllable intelligibility corresponds well to this parameter.
Support (ST) This is a acoustics parameter for players on the stage.
The Support is the parameter which focuses on the "ease of monitoring own sound". To obtain this parameter, the sound source is set at the point of musician on the stage and a microphone is set up at 1 m away from the musician.
The two parameters, ST1 and ST2 are proposed. ST1 is the parameter focused on the data until 100 ms after the arrival of the direct sound and ST2 is the parameter focused on until 200 ms.
Speech Transfer Index
(STI)
This is a parameter for estimating speech intelligibility.
The influence of the reverberation, the echo and background noise appears as the change of Modulation Transfer Function (MTF). STI is calculated from the MTF.
On the other hand, MTF can be calculated from the impulse response if the effect of background noise on MTF is ignored. In this software, STI can be calculated from the impulse response.
Lateral Efficiency (LE) Lateral Efficiency is the parameter which focuses on the energy of the reflected sound from lateral direction.
To calculate this parameter, it needs two kinds of impulse response, one is the response measured by an omni-directional microphone and the other is measured by the bi-directional microphone which set orthogonally to the hall.
Room Response (RR) The room response is similar to the LE, the parameter focus on the energy of the reflected sound from lateral direction.
The measurement method is the same to LE.
Early Ensemble Level (EEL) Compared with ST, this parameter focuses for "ease of monitoring played by others".
As in the method of ST, the sound source is set at the point of a musician on the stage and a microphone is set up 1 m away from the point and one impulse response is measured. Also, another microphone is set by another musician who listen the sound played by the player mentioned above.
Inter-Aural Cross Correlation (IACC) IACC is the cross-correlation between two signals which enter to the left and right ears.
The calculation of IACC needs the impulse responses measured at both ears by a HATS, head and torso simulator.
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